Nervous System
Chapter 7

The Nervous system is the master controlling
and communicating system of the body.

3 step process
◦ Sensory-uses sensory receptors to monitor changes
inside and outside of the body.
◦ Integration-processes and interprets the
information and makes decision about what to do
with the information (integration)
◦ Motor-activation of muscles or glands in response
to the stimuli
NERVOUS SYSTEM
Organization of the Nervous
System

All nervous system organs are separated
into two classifications by structure.
◦ Central Nervous System
◦ Peripheral Nervous System
Central Nervous System
(CNS)

Made up of the brain and spinal cord

Main purpose is to interpret the incoming
sensory information and relay tissue
instructions based on past experiences or
conditions.
Peripheral Nervous System
(PNS)

Anything in the nervous system outside of
the brain and the spinal cord.

Consists of mainly nerves
◦ 2 types
 Spinal Nerves- Carry impulses to and from the
spinal cord.
 Cranial Nerves- Carry impulses to and from the
brain.
Functional Classifications

The functional classification is only
concerned with the peripheral nervous
system
◦ Sensory/afferent- send information from the
sensory receptors to the CNS.
◦ Motor/efferent-carry impulses from the CNS to
the muscles and glands and initiate a response.
Motor Divisions

Somatic nervous system
◦ allows conscious, voluntary movement of
skeletal muscles.
◦ Not all muscular activity is voluntary
 Skeletal muscle reflexes-stretch reflex
◦ When a muscle spindle is stretched, it sends a message
to the brain telling the brain to contract the muscle to
prevent tearing.
 Patellar-tendon reflex
Stretch Reflex
Motor Divisions

Autonomic Nervous System
◦ Regulates events that are automatic or
involuntary
 Activity of cardiac muscles and smooth muscle
 Separated into two parts
◦ Sympathetic-fight or flight, produce reactions under
stress
◦ Parasympathetic-rest and digest, all other autonomic
functions, blood vessel dilation, pupil dilation.
Nervous Tissues
◦
Astrocytes
Abundant, star-shaped cells

Brace neurons to their nutrient
supply

Form barrier
between capillaries
and neurons

Control the chemical
environment of
the brain by picking up excess ions and recapturing released
neurotransmitters.
 Microglia
Spiderlike phagocytes that dispose of debris (dead cells)
 Ependymal

Line the cavities of the brain and spinal cord.

Their cilia help circulate CSF that fills those cavities
 CSF forms a protective cushion for the CNS

Oligodendrocytes◦ Produce a myelin sheath around nerve fibers in
the CNS
◦ Insulation/protection for nerves

Satellite cells
 Protect neuron cell bodies by cushioning
cells

Schwann cells
 Form myelin sheath in the peripheral
nervous system
Nervous Tissue: Support Cells
Structure of a Motor Neuron
Neuron Anatomy

Neurons = nerve cells
 Cells specialized to transmit messages
 Major regions of neurons
 Cell body – nucleus and metabolic
center of the cell
 Processes – fibers that extend from the
cell body

Body of the Cell
 Metabolic center of the neuron
 Nissl substance – specialized rough
endoplasmic reticulum
 Neurofibrils – intermediate cytoskeleton
that maintains cell shape
Neuron Anatomy

Extensions outside the cell body
 Dendrites -carry messages toward the
cell body
 Axons –carry messages away from the
cell body to another neuron
Neuron Anatomy
Axons and Nerve Impulses
Axons transmit their information at their
terminal ends.
 All axons branch out at their end forming
thousands of axonal terminals.
 Once the impulse reaches the axonal
terminal it stimulates the release of
neurotransmitters into the extracellular
space.


In Between each axonal terminal is a
small gap called a synapse.

Neurons never touch other neurons.
Synapse

Most long nerve fibers are covered with a
fatty material called myelin.
◦ It protects and insulates the fibers and
increases the transmission rate.

Axons outside of the CNS are insulated
(myelinated) by Schwann cells.
◦ Wrap themselves around axons for insulation.
◦ When it is wrapped around the axon, the
myelin sheath encloses the axon.
Neurons
The neurilemma is in between the myelin
sheath and the Schwann cells.
 The Myelin sheath is formed by many
different Schwann cells, this leaves gaps
of uncovered surface area that are called
Nodes of Ranvier.

Neurons
Myelin sheaths around the fibers are
gradually destroyed.
 Once destroyed they harden and become
“scleroses”
 This decreases the persons ability to
control their muscles and their mobility
decreases.

Multiple sclerosis
Clusters of neuron cell bodies and
collections of nerve fibers are named
nuclei when in the CNS.
 They are well protected in the body within
the skull or the spinal column.
 These cells do not go through cell division
after birth. If a cell dies, it is not
replaced. Thus the need for the bony
protective coverings.

Central Nervous System

Ganglia- small collection of cell bodies in the
CNS.

Tracts- bundles of nerves running through

White matter-dense collections of myelinated
tracts (fibers)

Gray matter-unmyelinated fibers and cell
bodies
CNS anatomy

Sensory Neurons
◦ Afferent-go toward the brain/spinal cord for
processing
◦ Transmit information about outside stimuli to
the CNS
◦ Cutaneous receptors-skin
◦ Proprioceptors- muscle/tendon
◦ Nociceptors- pain impulses
CNS
Detect the amount of stretch or tension in
skeletal muscles, tendons or joints.
 Information is sent to the brain so that it
can make adjustments for any changes in
posture/balance.

Proprioceptors

Motor Neurons◦ Efferent, carry impulses from the CNS to the
muscles/glands for action.
◦ Relay the action message to the muscles

Association Neurons◦ Also known as interneurons.
◦ They connect the motor and sensory neurons
in neural pathways.
CNS





Naked Nerve Endings- pain and
temperature
Messner’s Corpuscles- touch receptors
Pacinian Corpuscles-Deep Pressure
Golgi Tendon Organs (GTOs)proprioception (contraction)
Muscle Spindle-proprioception (stretch)
Sensory Receptors

2 major functions
◦ Irritability- ability to respond to a stimuli and
convert it into a nerve impulse
◦ Conductivity-ability to transmit the impulse to
other neurons, muscles or glands.
Nerve Impulses-Phyisology
When at rest, the plasma membrane is
polarized, meaning there are fewer
positive ions sitting on the inner face of
the membrane than on the outside.
 The major positive ions on the inside of
the cell are potassium (K+), and the
positive ions on the outside, are sodium
(Na+)
 If the inside is more negative than the
outside, the neuron remains inactive.

Physiology

Many types of stimuli are used to excite
the neurons, to activate and create an
impulse.
◦ Light excites eye receptors
◦ Sound excited some ear receptors
◦ Pressure for cutaneous receptors, etc.
Physiology

Regardless of the stimuli, the result is all
the same, permeability of the cell
membrane changes for a brief period.
◦ Once the neuron is activated, the sodium gates
of the plasma membrane open and allow the
sodium (Na+) into the cell.
◦ Law of diffusion- higher concentration of Na+
outside the membrane
◦ Once inside the polarity of the inside of the cell
changes, this process is called depolarization.
Physiology-depolarization

If the stimulus is strong enough, and the
rush of sodium is great enough, the
neuron is activated through
depolarization.
◦ Once depolarized the neuron will transmit the
nerve impulse (action potential).

**This process is all or nothing**. The
impulse will either be sent all the way
through the neuron, or not sent at all.
Depolarization cont.

Almost immediately after the Na+ ions rush
in, the membrane permeability changes
◦ It returns to being impermeable to Na+, but
permeable to K+, just as before.

Now the K+ ions are free to float back out
into the tissue fluid. This happens rapidly,
the quick outflow of these ions restores the
electrical conditions of the cell. Returning to
its resting (polarized) state. This process is
called repolarization
Repolarization
Action potential
Once an impulse is sent through the
neuron and it reaches the axonal
terminal, tiny vesicles containing the
neurotransmitter chemical fuse with the
axonal membrane, releasing the chemical
transmitters.
 These chemicals travel across the synapse
and bind to the next neuron.
 This will more often than not restart the
action potential in that next neuron.

Conductivity of Neurons

Reflexes- rapid, predictable and involuntary
responses to stimuli.

Autonomic reflexes-activity of smooth
muscles, heart, glands
◦ Salivary secretion, pupil dilation
◦ Digestion, blood pressure, sweating

Somatic reflexes◦ Any reflex that stimulates skeletal muscles
◦ i.e. hand on a hot stove
Reflex Arcs

The brain is the largest and most complex
mass of nervous tissue in the body.
◦ Made up of four major regions
 Cerebral hemispheres
 Diencephalon
 Brain stem
 Cerebellum
Central Nervous System
The largest of the four sections of the
brain.
 Covered in gyri, folds/ridges in the brain
tissue.
 The deeper grooves in the tissue are
referred to as fissures.

◦ These fissures separate the hemispheres into
lobes, these lobes are named for the cranial
bones that protect them.
Cerebral Hemispheres



Controls somatic sensory activity
Recognizes pain, cold or light touch.
Center for cognition, speech and visual
perception.
**the body’s sensory pathways are
crossed, meaning the left side of the
sensory cortex receives information from
the right side of the body and viceversa**
Brain Anatomy

Occipital Lobe-visual processing center
◦ Smallest of the four lobes of the brain
◦ Located in the rear of the skull

Temporal Lobe-center for auditory
processing
◦ Important in the processing of both speech and
vision stimuli
◦ Contains the hippocampus which plays a key
role in long-term memory.
Brain Anatomy

Frontal Lobe-Primary motor area of the
brain.
◦ Allows us to consciously move our skeletal
muscles.
 The axons of these motor neurons join together to
form the major voluntary tract, the cortico-spinal
tract, which connects to the spinal cord.
◦ Pathways are also crossed left brain controls
right side of your body…
Brain Anatomy

Broca’s area- located in the base of the
precentral gyrus in the frontal lobe
◦ Specialized area which allows us to speak.
Usually found in the left hemisphere.
◦ If damaged, your ability to speak is severely
handicapped. You know what words you want
to say, but are unable to vocalize them.

The frontal lobe houses the areas involed
with language (word) comprehension.
Frontal Lobe cont.

The higher level thinking/reasoning
centers are believed to be in the anterior
part of the frontal lobes.
◦ Complex memories are stored in the temporal
and frontal lobes.
◦ Speech areas are located in between the areas
between the temporal, parietal and occipital
lobes.
 the frontal lobe is involved with the areas of
language comprehension, meaning of words.
Brain Anatomy

The Corpus Callosum is a large fiber tract
that connects both cerebral hemispheres.
◦ It allows each hemisphere to connect with the
other.
 it increases function of the brain, because some
functions are controlled only by one side.
Brain Anatomy
White matter-myelinated tissue that
makes up most of the cerebral
hemisphere
 Gray matter-unmyelinated cells or cell
bodies of neurons found in the outermost
area of the cerebral cortex, the cerebrum.

Brain Anatomy

Most of the gray matter is found in the
cerebral cortex, but there are small areas
of gray matter found in the cerebral
cortex called the basal nuclei
◦ Helps control/regulate voluntary motor
activities by modifying the information sent
from the CNS to skeletal muscle.
Brain Anatomy
Also called the interbrain
 Found above the brain stem and is
covered by the cerebral hemispheres.
 Made up of the thalamus, hypothalamus
and the epithalmus.

Diencephalon
Encloses the third ventricle
 It is a relay station for the sensory
information from the periphery to the
sensory cortex.
 Helps interpret whether the stimuli we are
experiencing will be pleasant or
unpleasant.

Thalamus
Translated “under the thalamus”
 Key role in regulation of body
temperature, water balance and the
body’s metabolism
 Center for emotional drives

◦ Hunger, thirst, sex, pain and pleasure

Controls the pituitary gland and
mammillary bodies. Reflex centers
involved in olfaction.
Hypothalamus
Epithalmus forms the roof of the third
ventricle
 Key parts
◦ Forms the roof of the third ventricle.
◦ Pineal body-small gland that produces
melatonin, regulates your sleep/wake patterns
◦ Choroid plexus-knots of capillaries within each
ventricle, together it forms the cerebrospinal
fluid
Epithalmus
Approx. the size of a thumb in diameter,
and about 3 inches in length.
 Made up of the midbrain, pons and
medulla oblongata
 Provides a pathway for ascending and
descending tracts of the nervous system
 Also consists of many small gray matter
areas, which make up the cranial nerves.

Brain Stem
A relatively small aspect of the brain stem
 The cerebral aqueduct travels through the
midbrain connecting the third and fourth
ventricles.
 The anterior aspect of the midbrain is
composed of the cerebral peduncles
(means little feet of the cerebrum)

◦ The peduncles relay impulses to the PNS
Midbrain
The pons is a rounded structure that is
located just below the brain stem.
 Translated pons means bridge

◦ Bridge between brain and spinal cord.

Made up mostly of fiber tracts.
◦ Center for breathing control.
Pons

Most inferior part of the brain stem.
Merges with the spinal cord fluidly. Large
fiber tract, regulate visceral activities.
◦ Center for heart rate, blood pressure,
breathing, swallowing and vomiting.
Medulla Oblongata
Mass of gray matter which extends the
length of the brain stem.
 Involved in motor control of the visceral
organs.

◦ Reticular Activating System (RAS)- plays a role
in sleep/wake cycle.
 Damage to this area leads to a comatose state.
Reticular Formation
Large, cauliflower like area, consists of
two hemispheres like the cerebrum
 Provides precise timiing for skeletal
muscle and activity

◦ Center for balance and equilibrium
◦ Coordinated body movements

Center of autonomic activity
Cerebellum

Compare the brain’s intentions with the
actual output of muscular activity
◦ Balance is judged by body position and amount
of tension in muscles, etc.

If the cerebellum is damaged, direct blow
to the head, tumor, stroke, etc.
◦ Movements will become clumsy, disorganized
 Called ataxia
◦ People with ataxia are not able to perform
simple tasks such as placing your finger to
your nose with your eyes closed.
Cerebellum

Nervous system tissues are soft and delicate.
Thus the need for the mass amounts of
protection.
◦ CSF, skull, spine, etc.
◦ Meninges-outer layer of the dura matter
 Outermost covering of the brain.
◦ Arachnoid mater- middle layer of the meninges
 Span the subarachnoid space attach it to the innermost
membrane
◦ Pia matter-closest membrane to the actual brain
and spinal cord.
 Where the CSF is housed.
◦ **Meningitis leads to encephalitis**
Protection of the CNS

Continually formed from blood by the choroid
plexus.
◦ Clusters of capillaries hanging in each of the brains
ventricles.



Protects the brain and spinal cord as a watery
cushion
Constantly flowing/moving through the spinal
column and skull
Changes in the CSF can mean certain
diagnoses/problems
◦ Meningitis, tumors, MS
◦ Spinal Tap
CSF
Ventricles of the Brain
Brain thrives on a constant, homeostatic
environment
 Any slight change in stasis could result in
uncontrolled neural activity.
 Composed of the least permeable
capillaries in the whole body.

Blood Brain Barrier

Alzheimers- progressive degenerative
disease of the brain. Brain tissue
deteriorates and ultimately leads to
dementia.
◦ Shortage of acetylcholine (Ach) and structural
changes.
◦ Mostly attacks centers for cognition and
memory.
Brain dysfunction
Parkinsons- problem at the basal nuclei
 Results of the degeneration of the
dopamine releasing neurons.
 This causes constant tremors, shuffling
gait and they have trouble initiating
muscular movement

Brain dysfunction
Huntington’s- degeneration of the basal
nuclei, which leads to cerebral cortex.
 The early stages are marked by wild,
uncontrollable flapping movements of the
limbs.
 Later in the disease mental deterioration
occurs.
 Usually fatal within 15 years.

Brain Dysfunction
Concussion- direct blow to the head,
minor symptoms, dizziness, impaired
vision, no permanent brain damage
occurs.
 Contusion- Bruise, marked tissue
destruction/deterioration of the cerebral
cortex. Usually results in loss of
consciousness.

Traumatic Brain Injuries

Concussion grades-
◦ Grade 1-no loss of consciousness, appears
dazed or confused (bell rung)
◦ Grade 2-headache and confusion/vision
impairment lasting longer than 1 minute.
 Possible loss of consciousness
 Changes in cognition and emotional state,
irrational.
◦ Grade 3- Loss of consciousness for more than
one minute, exhibit more extreme symptoms
than grade 2.
Concussions
Approximately 17 inches long, pathway
for both afferent and efferent impulses.
 Very well protected by the vertebrae and
CSF.

◦ 7 cervical vertebrae
 Atlas-C1-supports the skull
 Axis-C2-allows for rotation
◦ 12 thoracic vertebrae
◦ 5 lumbar vertebrae
Spinal Cord